When an area of an image to be treated is larger than the image forming device, or the image medium cannot be loaded or inserted into the device, the device must be moved relative to the medium.
Hereinafter the term “image forming device” includes a variety of scanners, different surface mapping devices, surface inspection devices, printers (including those using inkjet, thermal and laser printing), plotters, marking and engraving devices, image-wise material deposition or removal devices, which are intended to read an image from, or to apply an image to, an image medium, such as paper, transparencies, fabrics, plastics, glass, metals and the like.
The term “image forming means” is used hereinafter to include any of an operating means for: forming an image-wise surface marking or altering, or printing image on the medium, or making any image-wise material deposition on the surface or removal from the surface, or scanning surface image, or mapping surface structure, or measuring any local properties of the surface material and saving of an electronic image in the computer memory, etc, or combination thereof. Here “surface altering” denotes the chemical, physical or positional particle alteration of a medium at its surface.
Inkjet printing mechanisms print images using inkjet cartridges, often called “pens,” to shoot drops of ink onto a page or surface of print media. In multi-color cartridges, several print heads and reservoirs are combined into a single unit, with each reservoir/print head combination being used for a given color. Each pen has a print head formed with very small nozzles through which the ink drops are fired.
Thermal printers typically interpose a donor sheet that includes donor material and a backing between a thermal print head and the printing surface. The thermal print head includes an array of thermal printing elements. The thermal print head prints by pressing the donor sheet against the printing surface and selectively energizing the thermal printing elements of the array, thereby selectively transferring pixels of donor medium from the donor sheet to the printing sheet.
To print an image, the print head is propelled through a print zone back and forth across a page and, by selectively energizing the printing array elements as the print head moves and the colorant is expelled in a pattern on the print surface to form a desired image. The printing elements (nozzles in inkjet printers and thermal elements in thermal printers) are typically arranged in linear arrays (in inkjet printers usually located side-by-side on the print head, parallel to one another), and perpendicular to the scanning direction of the print head, with the length of the arrays defining a print swath or band. Thus, if all the elements of one array were continually energized as the print head made one complete traverse through the print zone, a band or swath of pixels would appear on the sheet. The width of this band is known as the “swath height” of the pen, the maximum pattern of ink that can be laid down in a single pass. The print media, such as a sheet of paper, is moved through the print zone typically one swath height at a time, although some print schemes move the media incrementally by, for instance, halves or quarters of a swath height for each print head pass to enhance the appearance of the final image.
However a printing mechanism is configured, drop placement on the media must be coordinated with the incremental advance of the media through the print zone for sharp, vivid images and text, which are free of print defects, such as pixel banding, improper spacing, and printed line overlapping. Many types of printing mechanisms use a series of conventional paper drive rollers or tires to frictionally engage the print media and incrementally advance the media through the print zone, moving either a full or fractional swath width.
Other image forming devices include scanners which have a scan head with image receptors that “read” an image previously printed on media, and convert this image into a memory file, which may then be computer edited or sent to a selected destination. The image receptors in a scan head may be a series of discrete elements arranged in a linear array. These image forming scanning mechanisms may use the same media advance system as described above for an inkjet printing mechanism, and indeed, in many multi-function devices the same media advance system is used for both printing and scanning.
Using a more general concept, both inkjet print heads and scan heads may be considered “image forming heads,” with print heads forming an image by printing that image on media or/and scan heads forming an image by “reading” an image that already exists on media. This generic image forming head may have one or more arrays of discrete interaction elements arranged, for instance, in a linear array, to selectively interact with media in an interaction zone of the image forming device. For an inkjet printing mechanism, the interaction elements are ink-ejecting nozzles and the interaction zone is a print zone. For a scanning mechanism, the interaction elements are image receptors and the interaction zone is a read zone.
Regardless of the technology utilized, a conventional image forming device is typically fed with a medium. The approach to feeding the medium dictates the minimum size of the image forming device. For example, in order to print onto a paper of letter size (e.g. 21.59 cm×27.94 cm), a stand-alone printer must be at least 21.59 cm wide to accommodate the letter-size paper. Since the medium must be fed into an image forming device, an image cannot be transferred to or received from a rigid substrate or other medium that cannot be fed into the stand-alone image forming device. Technologies for image forming on the rigid substrate are available.
For large surfaces, it is preferable to use an apparatus moving across the surface. An image forming device moving across the work surface can be made much smaller than the conventional image forming device and can operate on a greater variety of media.
The disclosures of all the referenced patents hereinafter are hereby incorporated herein by reference in their entirety as if set forth fully herein.
One type of a moving image forming device is a self-propelled precision device incrementally moving in predetermined fashion, for example, as described in U.S. Pat. No. 6,695,445 to Hagstrom, et al. This patent relates to a printer for printing large area sheets of print media or substrates, such as posters, where the print media remains on a flat support and a standard print head is driven across the surface as it prints. The print media or substrate remains stationary and can be supported on a suitable table. Once the printer frame, print head and print medium are oriented at a reference or home position, the frame moves across the print medium substrate uniformly to provide for transverse movement of the printer for printing the images (such as a poster or graphic print) under a printer control. The printer frame is incrementally driven along the entire length of the sheet to complete the print job. High friction material rollers are utilized for driving against the printing surface. The program control for the printing program can be a program in a personal computer or other computer operating in a known manner. The printer frame can be supported on or guided by rails and the drive members can engage the rails for driving.
This invention has some serious drawbacks. The frame engages the printing surface by rollers of high friction material. Any vibrations or other disturbances may produce small alterations in the frame position relative to the printing surface during printing process and prevent high accuracy printing. The sources of the vibrations and other disturbances may be exterior or interior (e.g. motors for driving the frame across the printing surface or the rather heavy print heads reciprocating over the frame shaft).
Also, there are no provisions for translational displacement of the frame from line to line. A small difference in roller friction in different locations of the long frame may alter the frame direction. Lateral guide rails may be used to help prevent drift of the beginning of the print line, but it cannot help small changing shaft directions, which is rather critical to proper printing. Presuming a printing resolution 200 DPI and poster width 24 inches, a change of 0.02 grads in shaft direction as the frame is moving to the next line, will lead to “white” gap between lines, which can be discerned by the eye. Such a printer has no service station for treating nozzles of inkjet print heads in the course of printing. The provision of the service station is essential, especially for printing a big size picture. Adding a service station to such a construction can be difficult, as it has to be on the moving frame and its operation will provide another strong disturbance source in the frame position stability, as the frame is not fastened to the work surface.
U.S. Pat. No. 6,805,504 to Nisnevich proposes a device for incrementally moving across a work surface and capable of carrying operating tools.
The term “operating tools” denotes any image forming means as well as cutting means, pointing means, digitizing means, means treating the surface at specific points, etc., and shall be used herein to denote same. The device is based on a motion engine using two cams to advance the device and an additional two eccentric cams to change the parts of the device that bear against the work surface and using telescopic legs supporting the device. The device comprises two parts reciprocating one relative to the other. One part carries the image forming device. Each part is advanced in turn by the pair of the cams. The advancing part is suspended over the bearing surface supported by another part resting on the surface.